“I don’t understand the normal function on patch bays. Specifically, what is the difference between normal and half-normal, and when would I use one over the other?”
First, check out the definitions in our WFTD archives. The distinction should be clearer once you read those. In order for any of it to really make sense, however, you have to understand why you would want any normalled connections at all. The most effective studio wiring/patch bay designs will have the patch bay set up so it automatically routes signals to their most likely destinations. For example, if the output of your keyboard module is “normally” routed to channel 16 then you probably want to set up your patch bay so that connection is made automatically, meaning you don’t have to patch a cable between where the module is on the bay to the channel input. It’s already internally done in the bay. This is known as normalling
If a patch is going to be automatically done inside of a patch bay then clearly it is important to be able to override that in case you need to route that signal somewhere else or use those inputs for something else. Thus, on a properly configured patch bay, when you plug another source into the patch point for input channel 16, as in the example above, the signal coming from the module to that point would be automatically interrupted (cut off) in favor of the signal coming in on the patch you just made. Very convenient, and one of the reasons why patch bays are so important in a working studio. So what happens to the signal coming from the module? It’s still available at its own patch point and can still be routed to another destination if need be.
Once you get the general understanding of what a normal patch bay connection is and why it is important you can then begin understand the distinction between half-normal and normal (often called full normal). We’ll explain. Most patch bays have two rows of jacks, one above the other. The normal wiring convention is that outputs are on the top row and inputs are on the bottom. Outputs normally feed inputs so this logic makes sense. That module’s output would therefore appear at a jack on the top row. The corresponding channel input would appear on the jack immediately below. If they are normalled you know you do not need to make a patch for the module to feed into that input. The only question is, what conditions will break this connection? This is the difference between full normal and half-normal. If those points are wired to be half-normal then the connection between that module and the inputs will ONLY be broken when a cable is plugged into the bottom jack (the channel input jack). Plugging a cable into the top jack (the module output) will NOT break the connection. The signal will still flow down to that channel input and simultaneously appear at the end of that cable you plugged in. This effectively creates a Y cable. Now, go back and read those WFTD entries again and they should make more sense.
Why would you use one over the other? The only time you really need a half-normal is when you might need to split a signal to two places. Since there is often very little downside to a half-normal you can deploy these almost anywhere you would use a full normal, even if there is only a very slight chance you might ever need the half-normal function. There are many possible examples where each is used. An interesting application of the half-normal is mixing board insert points. Here, you would have the send on the top jack and the return on the jack right below it. Without anything plugged in the signal flows through without interruption, just like your board “normally” works. If you want to insert a compressor or EQ you will use both jacks (one for sending the other for returning) so regardless of whether it is set up as half or full normal it will work the same. However, in a half-normal configuration that top jack (the send) can double as a direct out, which you can use to go to a recorder or an effects processor without interrupting the signal’s path on through the mixer. You just leave the bottom jack open for this to work.
An example of where you would probably want a full normal is when you are bringing microphone signals into a mixer through a patch bay. If you need to patch the mic’s signal over to another input channel, or to an outboard preamp, you do not want it to remain connected to its normal channel, as would happen in a half-normal configuration.